1. Field of the Invention
The present invention relates to a data communication apparatus for effecting data communication after sending out a dialling signal.
2. Related Background Art
There is already known a facsimile apparatus which is capable of calling a destination station and thereafter automatically effecting facsimile communication. In the facsimile communication, it is customary to set a time for initial identification (TI) for detecting an effective response signal from the destination and to inspect the expiration of said time by so-called TI timer.
It is also already known, at making a call, to enter or store in advance pause data for determining the timing of start of facsimile communication, in addition to the telephone number data.
FIG. 6 shows the sequence of signals in call making in a conventional facsimile apparatus, wherein the left-hand side shows the signals from the calling (image transmitting) side while the right-hand side shows the signals of the called (image receiving) side.
As shown in FIG. 6, the calling side transmits dial data (tone or pulse signals) A corresponding to the telephone number, and then CNG signals.
The called side, in case of automatic reception, switches the line to the facsimile unit, and, upon detection of the CNG signal, transmits a protocol signal (such as DIS) of the called side.
FIG. 7 shows a case of providing a pause period according to pause data entered in advance. A pause period D is provided after the transmission of the dial data. In the illustrated example, there are inserted three pause periods of a unit length each, corresponding to three sets of pause data.
At a pause digit, the conventional facsimile apparatus interrupts the transmission of dial data and does not transmit any signal to the telephone line (D in FIG. 7).
The TI timer is started after the transmission of all digits (including pause data), as indicated by C in FIG. 7. The transmission of the CNG (facsimile call) signal is started after the start of said TI timer.
In an overseas automatic call, plural pause periods are automatically set or registered by the user at the end of dial data as shown in FIG. 7, in order to prevent the transmission from being inhibited by the overflow of the TI timer as the connection time is longer in such call.
However, in such conventional structure, if the receiving side is a facsimile apparatus with automatic telephone/facsimile switching function, the detection of the CNG signal is delayed by the time of the pause period inserted by the calling side, because the CNG signal transmission is started after the processing of the pause digit. Also if the CNG detecting period of the receiving side overlaps with the pause period of the calling side as shown in FIG. 7, the receiving side may mistake the call as a telephone call, whereby the facsimile communication may be terminated by an error ending.